probably guessed dude.
they run through number sequences like marketing companys do ph numbers
http://www.totse.com/en/bad_ideas/scams_and_rip_offs/cardalgo.htmlAs some of you know, the credit card companies (Visa, MC, and American
Express) issue card numbers which conform to a type of checksum algorithm.
Every card number will conform to this checksum, but this is not to say
that every card number that passes this checksum is valid and can be used,
it only means that such a card number can be issued by the credit card
company.
Often this checksum test is used by companies which take credit cards for
billing. It is often the first step in checking card validity before
attempting to bill the card, however some companies stop here. Some
companies only check the first digit and the card number length, others use
this very convenient algorithm, while others continue on to check the bank
ID portion of the card number with a database to see if it is a valid bank.
These tests are designed to weed out customers who simply conjure up a card
number. If one were to try to guess at an Amex number byusing the right
format (starts with 3 and 15 digits long), only about 1 in 100 guesses
would pass the checksum algorithm.
Why do companies use the algorithm for verification instead of doing an
actual credit check? First, it's much quicker (when done by computer).
Second, it doesn't cost anything. Some credit card companies and banks
charge merchants each time they wish to bill or verify a card number, and
if a merchant is in a business where a lot of phony numbers are given for
verification, this can become rather costly. It is a known fact that most,
if not all, online services (i.e., Compuserve, Genie, etc.) use this method
when processing new sign-ups. Enough said about this, you take it from
here.
The majority of transactions between credit card companies and merchants
take place on a monthly, weekly, or bi-weekly basis. Such bulk
transactions are much less expensive to merchants. Often a company will
take the card number from a customer, run it through the algorithm for
verification, and bill the card at the end of the month. This can be used
to your advantage, depending on your situation.